1. Field of the Invention
The present invention relates to a method for producing a semiconductor optical device.
2. Related Prior Art
A Japanese patent application published as JP-H10-242563A has disclosed a method for manufacturing a semiconductor optical device that includes a semiconductor layer containing aluminum (Al), a mesa structure extending along a [011] orientation, a cladding layer covering sides of the mesa structure and formed by the mass transportation, and a semiconductor layer covering the sides of the mesa and burying the mesa structure. The method disclosed therein provides a first step for forming the mesa structure, a second step for carrying out the mass transportation until the side of the cladding layer appears a surface with the {111} planes, and a third step for forming a semiconductor layer to bury the mesa structure.
An United States patent U.S. Pat No. 5,093,278 has disclosed a method for producing a semiconductor optical device having a buried mesa structure, which includes a first step of sequentially growing a first cladding layer, an active layer, a second cladding layer and a cap layer, a second step for forming a mask with a striped plane shape, a third step for etching, by using the mask thus formed, the cap layer with an etchant first and the other semiconductor layers with another etchant until a portion of the semiconductor substrate exposes, and a fourth step for selectively forming a blocking layer in both sides of the waveguide region etched in advance.
Those semiconductor optical devices appeared in the patens mentioned above have the structure for burying the mesa structure. This configuration to bury the mesa structure enhances a performance of the device. However, the buried structure strongly depends on the cleanness of the surface on which the burying layer is grown and/or the cross section of the mesa structure.
The method disclosed in the Japanese patent application published as JP-H10-242563A is hard to realize a stable surface with the {111} planes on both sides of the mesa structure with the normal trapezoidal cross section. Thus, a simplified method has been desired. The present invention is to provide a method for manufacturing a semiconductor optical device, where the unevenness of the burying of the mesa structure can be reduced.